Vacuum Induction Casting Research Articles

Design and development of large-diameter Mg-Zn-Ca bulk metallic glass for biomedical applications: A mechanical and corrosion perspective

Being amorphous, bulk metallic glasses (BMGs) exhibit superior properties compared to their crystalline alloy counterparts. Amorphous materials are preferred for their excellent mechanical and degradation behavior. Among the various elemental combinations, MgZnCa has shown the most promising results, as evidenced by the literature. However, the maximum achievable size of the metallic glasses remains a bottleneck. The current work aims to address this challenge and achieve it splendidly with a systematic methodology by developing larger diameter MgZnCa BMGs through vacuum induction casting using a specially designed copper mold. The optimal composition was formalized for glass formation of the Mg65Zn31Ca4 system using the CALPHAD technique. As a result, a 6.5 mm diameter glassy alloy was successfully obtained. The XRD and TEM analysis experiments demonstrated a perfect amorphous structure of the developed sample. The anti-corrosion properties of the as-cast glass increased, followed by enhancement in the yield strength and hardness in contrast to the properties of the human bone. Furthermore, the surface wettability analysis showed an adequate surface obtained to promote fibroblast adhesion. In conclusion, the current work represents a notable progress in the fabrication of larger-diameter MgZnCa BMG for biomedical applications, considering that the biggest diameter ever reported in the MgZnCa system was more than a decade ago.

Developing austenitic high-manganese high-carbon steels for biodegradable stent applications: Microstructural and mechanical studies

Fully degradable stents that temporarily support healing tissue can solve potential long-term complications associated with permanent implants. In this study, we investigate austenitic high-manganese high-carbon steels as promising candidates for such biodegradable stent applications. The microstructural characteristics and mechanical properties of the Fe–Mn–C steels were systematically analysed to assess their suitability for this purpose. A series of four austenitic Fe–Mn–C steels with varying manganese (15 and 30 wt%) and carbon (0.6–1.0 wt%) content were processed by vacuum induction casting, annealing and hot forging. Microstructural analysis was performed, and the hot forged materials were further evaluated using ultrasound, macro hardness, and (stopped) quasi-static tensile tests to assess stent-related parameters. In contrast to the as-cast state, the hot forged steels exhibited high chemical homogeneity, as was found by energy-dispersive X-ray spectroscopy (EDXS). Electron backscatter diffraction (EBSD) revealed comparability between the four steels regarding their annealing twin fractions and grain size distributions. An austenitic microstructure was revealed for all modifications by transmission X-ray diffraction (XRD), except Fe–15Mn–0.6C, which displayed a minor ε–martensite fraction. Reducing manganese from 30 to 15 wt% resulted in favourable effects, including a higher Young's modulus, lowered offset yield strength, and an increased ultimate tensile strength due to larger strain hardening while preserving a high total elongation. However, reducing the carbon content to 0.6 wt% diminished the mechanical performance due to reduced solid solution strengthening and the ε–martensite formation. Among the investigated steels, the novel Fe–15Mn–0.8C alloy exhibited the most attractive combination of the studied properties for potential stent applications.

Effect of Aluminum Content on Interfacial Reaction of Directionally Solidified TiAl Alloys

Abstract High Nb-containing TiAl alloys with different aluminum content were prepared by vacuum induction casting technology, and then processed via directional solidification in a Y2O3-coated Al2O3 crucible. The effect of aluminum content on the metal and coating interface, chemical composition, and phases at the interfaces were evaluated. The variations of microhardness of the samples from surface to interior were presented. The results showed that there is no significant difference between the matrix structure of TiAl alloy with different aluminum content. Nevertheless, with increasing aluminum content in the melt, the thickness of the reaction layer decreased. Moreover, the elements diffusion distance and hardness also showed an apparent decrease with the increasing of aluminum content. Besides inherent phases in the melt, simultaneous precipitation of Al2O3 particles also occurred.

Nickel Alloys in Directionally Solidified State – Characterisation of Microstructure and Phase Composition of the Alloys

The paper deals with the characterisation of the structure and phase composition of selected types of nickel alloys. Experimental alloys were prepared by vacuum induction casting. Castings were directionally solidified in corundum tubes with specified apex angle in the two-zone crystallisation furnace. Rate of directional solidification was 100 mm/h. Observation was carried out on the samples in the as-cast and directed state. Influencing of the structure by the process of directional solidification is evident. Porosity and micro-hardness were determined in transverse and longitudinal sections of individual samples and character of the formed structures was evaluated. Microstructural characterisation of materials was performed with use of scanning electron microscope. Distribution of individual elements was captured on X-ray maps, which documented significant chemical heterogeneity of investigated samples. Matrix composition corresponds approximately to the nominal composition of the alloys. The alloys contain moreover with variable content of primary and alloying elements. In the alloys with molybdenum and zirconium the phase enriched by these alloying elements were detected. On the other hand chromium is evenly dispersed in the basic matrix and it does not accumulate in the phases.

Investigation of Uranium Content in Russian Federation Beryllium

The uranium content in different Russian Federation (RF) beryllium grades and semi-products of different history has been investigated. Additionally, an investigation of the U content in two beryllium grades (S-65C and S-65B) produced by Brush Wellman (USA) has been performed for comparison. The influence of different technological steps of Be fabrication (vacuum induction casting and vacuum distillation) on the efficiency of Be purification from U impurity is analyzed. The U content influence on the activation of beryllium is also considered.

Dilatometry determination of phase transformation temperatures during heating of Nb bearing low carbon steels

Strengthening by precipitation and grain refinement using microalloying elements in combination with controlled rolling technique is the optimum solution when high strength, combined with excellent toughness, is required. Niobium in solid solution retards the diffusion-controlled process like onset of recrystallization and changes the transformation temperatures. Therefore, it is necessary to determine the effect of different Nb content on the transformation temperatures. Many dilatometry tests were carried out to determine the transformation temperatures. Three steel alloys were prepared by vacuum induction casting containing 0.0, 0.02 and 0.05 wt% Nb followed by flat hot rolled at 1200 °C with 90% reduction in thickness. In order to determine the transformation temperatures, temperatures were measured during continuous heating. The dilatation tests were carried out and the specimens were austenitised at 1175 °C to dissolve NbC sufficiently and then quenched to different transformation temperatures. The temperatures were determined from the deviation of dilatation curves. The TTT curves for low carbon steel containing Nb are plotted. It is obvious that increasing the Nb content up to 0.05 wt% increases phase transformation temperatures. Nb carbide dissolution temperature and wide of the temperature range of phase transformation at high temperature increase with increasing Nb content.

472. Vacuum induction casting of beryllium: J L Frankeny, Modern Castings, 45(6), 1965, 348–352

472. Vacuum induction casting of beryllium: J L Frankeny, Modern Castings, 45(6), 1965, 348–352